The present invention relates to electrically addressable light detector arrays acting in cooperation with planar light modification arrays to effect random access optical memory systems. The most common technology employed for optical memory systems is the read only optical disk. Video, audio or other information is written or encoded onto the disk in the form of localized variations in the surface topography or optical characteristics. Pulsed high power laser bursts are usually used to cause intense surface heating on the disks thereby melting, ablating or otherwise altering the disks in the form of micron sized spots. The difference between the transmissive and reflective optical characteristics of the spots relative to the unaffected surface constitutes a bit of digital information. Two concepts representative of such optical-characteristic modification techniques are described in U.S. Pat. No. 4,876,666 to H. Imai, K. Okada, and M. Tadokoro and U.S. Pat. No. 4,896,314 to W. Skiens, M. Lind, J. Hartman, J. Swanson and N. Iwamoto. The information is organized into a helical or spiral pattern and subdivided into sectors. By directing a light beam, usually a low power laser, onto the optical disk and observing the reflected or transmitted beam while rotating the disk and while radially positioning the light source, the total surface of the disk can be examined or interrogated. Examples of this reading technology are presented in U.S. Pat. No. 4,868,804 to F. LeCarvennec, D. Lecomte, D. Leterme and P. Romeas and U.S. Pat. No. 4,912,697 to M. Enari and other coinventors. Because of the small spot size, limited typically by the focusing properties of the recording laser beam, optical memories or recordings constitute the highest bit density technology available. This technology, however, is presently limited in its reading speed which is determined by the rotational velocity of the disk and the mechanical radial positioning speed of the reading laser source. Because of the relatively large inertial masses of the rotating disk and the moving laser head, positioning, or access, times are in the millisecond range. Bit data can be read out in a serial fashion, however, at megahertz rates.
Recently, additional storage dimensionality has been disclosed in the wavelength information concepts in U.S. Pat. No. 3,896,420 to A. Szabo and U.S. Pat. No. 4,101,976 to G. Castro, D. Haarer, R. MacFarlane and H. Trommsdorff. These techniques, characterized as frequency selective storage memories, operate by providing selectable narrowband light absorption in elemental regions of a two-dimensional material as determined by a focussed laser spot. The term hole-burning is used to describe the frequency selection process and requires a laser tunable on the frequency scale. Because the phenomenon is short-lived the system requires constant regeneration and operation at cryogenic temperatures. Furthermore the regeneration process requires high laser power levels while the reading process uses low laser power levels therefore necessitating two lasers. The rather demanding technological requirements for this optical memory system seem to preclude its implementation except for the most sophisticated applications.
Another three-dimensional random access optical memory system has been disclosed by L. Cooper, L. Ii and D. Shang in U.S. Pat. No. 3,868,652. This concept is ferroelectric based and uses refractive index tailoring by electric field means to achieve information storage. The individual ferroelectric memory sites are served by conductor lines and a photoconductive layer to provide localized field generation thereby modifying the local index of refraction of the addressed memory cell. Addressing requires both electrical and optical selection. Optical irradiation is accomplished in polarized narrowbeam fashion with a planar x-y position addressable matrix array of ferroelectric shutters. Fabrication complexity deriving from multi-layer ferroelectric construction and associated requisite electrical addressing lines seems to have precluded competitive manufacturing viability of this system.